Your thoughts on Colt are sound. BCM's midlength ARs which are equal to Colt but offer the midlength gas system in a 16" barrel instead of Colt's carbine length gas.
Either are excellent choices. Just to toss something new into the mix, I had an opportunity to shoot, disassemble and inspect a Scionics "Patrol Rifle I"
. I was pleasantly surprised with this 16" barrel /mid-length gas system rifle. I found the sample to be quite accurate and very well built. NP3 Bolt carrier, Magpul furniture and BUIS, 5lb single stage trigger and all built to milspec. A bit more than a grand, but I think, in the increasingly deeper sea of ARs, worth taking a look.